The present invention relates generally to a closed molding process that produces cured composite parts, and more particularly, to a method for producing multiple composite parts via resin transfer molding in a single cycle.
Resin Transfer Molding (RTM) is a process that uses a closed mold to produce cured composite parts. A dry fabric preform is placed in the mold cavity, the mold is closed and a resin in injected into the mold. The mold is exposed to an elevated curing temperature, and after a predetermined curing cycle has elapsed, a finished part is removed from the mold. The part is then ready for final trim.
Prior RTM processes are only capable of producing one composite part for each cycle. Therefore, after each cycle the RTM molding tool must be cleaned or reprocessed for the next injection.
Another disadvantage of the known RTM processes is the cost of low-tolerance tooling Typical aerospace applications for RTM, for example, will require a part to be formed to a predetermined thickness within about xc2x10.025 mm (xc2x10.001 in.). As those skilled in the art will readily understand, the fabrication of the tooling having this capability is relatively expensive, often costing 20-35% more than similar tooling having more open tolerances.
Accordingly, there remains a need in the art for an RTM tool and method that is capable of producing a plurality of highly consistent molded parts in a single molding cycle that overcomes the aforementioned drawbacks.
The Resin Transfer Molding Multi-Part/Shim Tooling (RTM-MPST) process overcomes this disadvantage by injecting resin into the mold cavity thus flooding multiple parts and shims, the pressure is distributed hydrostatically (evenly in all directions). This distributes the tolerance across each of the parts and with more shims in the cavity, the closer the parts will be to nominal thickness in a cost effective manner.
In one preferred form, the present invention provides a method for forming a plurality of composite parts via resin transfer molding in a single molding cycle. The method includes the steps of providing a mold having first and second mold members that cooperate to define a mold cavity; providing a plurality of shims; loading a plurality of preform workpieces into the mold cavity such that at least one of the shims is disposed between each of an adjacent pair of the preform workpieces; injecting a liquid resin into the mold cavity; curing the liquid resin to thereby form a cured workpiece matrix that is composed of a plurality of semi-finished composite parts and the at least one shim; and separating the plurality of semi-finished composite parts and the at least one shim from one another.
In another preferred form, the present invention provides a mold apparatus for performing a resin transfer molding operation on a plurality of preform workpieces to substantially simultaneously mold a plurality of semi-finished composite parts in a single molding cycle. The mold apparatus includes a first mold member, which defines a first mold line, a second mold member, which defines a second mold line, and at least one shim. The second mold member cooperates with the first mold member to define a mold cavity that is bounded by the first and second mold lines. The shim(s) are sized to fit within the mold cavity and are configured to be spaced in relation to the first and second mold lines to thereby segregate the mold cavity into a plurality of sub-cavities. Each of the sub-cavities is configured to house one of the perform workpieces. With the present invention, (RTM-MPST) produces multiple composite parts in one cycle thereby reducing the frequency that the tool is reprocessed and reduces resin waste.